The present invention relates generally to a power strip and more particularly to a power strip which provides ground fault protection.
Power strips are well-known and are commonly used in the art to provide a plurality of ancillary outlets for a single conventional wall outlet.
Power strips are typically constructed to include an plastic or metal casing which is at least partially hollowed out so as to form an interior cavity. The casing is mounted onto a first end of a power cable, said power cable including a hot line, a neutral line and a ground line which are all wrapped together by an outer protective sheath. The second end of the power cable is typically in the form of plug which is adapted to connect with a conventional wall outlet.
Each outlet in the power strip includes a first female contact receptacle which is electrically connected to the hot line of the power cable and a second female contact receptacle which is electrically connected to the neutral line of the power cable. Each of the first and second female contact receptacles is disposed within the interior cavity and is accessible through an associated slotted opening formed in the top of the casing. Optionally, each outlet in the power strip may include a third female contact receptacle which is electrically connected to the ground line of the power cable, the third female contact receptacle being disposed within the interior cavity and accessed through an associated opening formed in the top of the casing.
As such, each outlet is adapted to receive the plug of a device, such as an electrical appliance, which receives current from a power source. Specifically, each contact receptacle of an outlet is adapted to receive an associated contact terminal of the plug. As a result, a current path is established between the outlet and the plug, thereby providing the device with the necessary power to operate.
A power switch is commonly mounted onto the casing and electrically connects the hot and neutral lines of the power cord with each of the individual outlets. As such, the power switch allows for manual regulation of the flow of current between the power cord and each of the individual outlets. The power switch may be provided with an internal circuit breaker which monitors the amount of current passing into and traveling out from the individual outlets. Whenever the amounts of incoming and outgoing current passing into and traveling out from a load connected to the power strip exceeds the current rating of the circuit breaker (thereby signifying a dangerous overcurrent condition) or if there is an accidental short circuit in the load, the circuit breaker opens, or trips, thereby instantaneously cutting off the flow of electricity to the load, which is highly desirable.
Power strips are also commonly provided with surge protection capabilities. Specifically, a surge protector is often disposed within the interior cavity of the casing and electrically connects the hot and neutral lines of the power cord with each of the individual outlets. Connected in this manner, the surge protector protects any load connected to the power strip from a power surge occurring at the wall outlet. A power surge (also commonly referred to as transient voltage) is an increase in the voltage at the wall outlet which is above the standard level (e.g., 120 volts). As can be appreciated, subjecting a load to a power surge can potentially damage and/or destroy the load, which is highly undesirable.
Although widely used in commerce, conventional power strips of the type described above suffer from a notable drawback. Specifically, although conventional power strips provide protection from power surges and overcurrent conditions, conventional power strips do not provide protection from ground fault conditions.
A ground fault condition occurs if the current in the hot line and the current in the neutral line have unequal values (e.g., if the hot line connects directly to ground). As will be described further below, a ground fault condition can be extremely dangerous to a person who is in contact with the load. Specifically, if someone accidentally touches (i.e., grounds) the hot line, the current level in the hot line will immediately become less than the current level in the neutral line. However, because the current path from the wall outlet to the load effectively functions as a closed circuit, the current level in the hot line will always adjust to the current level in the neutral line. As a result, once the hot line is grounded, the current level in the hot line will quickly surge to the current level in the neutral line. This surge in current in the hot line can potentially electrocute the person contacting the load, which is highly undesirable.